1. FIELD OF THE INVENTION
The present invention relates to a source for generating electrons, and more particularly to a thin-film cold cathode structure which may be used for a planar display, an imaging tube, a vacuum tube, an electron line lithography, and an analyzing apparatus.
2. DESCRIPTION OF RELATED ART
There have been conventionally known cold cathode devices of various types such as a field emission type, a tunnel type, and an avalanche type.
As shown in FIG. 1A, in the field emission type of cold cathode device, electrons are emitted from a tip of a conical emitter corn formed on an emitter chip by using a gate field. However, this type of cold cathode device has some difficulty in stably emitting electrons, because the emitter corn may be damaged when ionized particles collide with the emitter corn and the absorbed particles act to lower the strength of an electric field at the tip of the emitter corn. To overcome this difficulty, it is necessary to disadvantageously locate the cold cathode device in a super high vacuum. Further, to obtain large electron current, it is also necessary to disadvantageously prepare a large number of lot of emitter chips and implement a complicated technique for a fine structure.
Turning to FIG. 1B, in the tunnel type of cold cathode device, the electrons which pass through a thin insulating film by the tunneling effect are emitted. To bring about the tunneling effect, the insulating film is required to be far thinner. In actuality, however, it is difficult to manufacture an extremely thin insulating film. Further, the thin insulating film is not stable in characteristic and in rapid in degradation.
Turning to FIG. 1C, in the avalanche type of cold cathode device electrons are emitted from part of a current that flows through a reversely-biased p-n junction of a diode. Disadvantageously, however, the efficiency is very low in emitting the electrons from the diode current that flows through the p-n junction. Like the field emission type device, electrons are emitted in a dotted manner. To obtain planar electron emission, therefore, it is necessary to integrate this avalanche type of cold cathode device. This means that it is difficult to extend this type of cold cathode device over the large area in light of the integrating technique.
In addition to the foregoing disadvantages, the conventional cold cathode devices suffer from large fluctuations of the emitted electron current, and the electron current changes in time. Hence, they cannot provide stable operation. Moreover, the conventional cold cathode devices do not have a long life, and some types of the devices require a complicated manufacturing process. This results in disadvantageously lowering their yield and thereby raising the manufacturing cost.